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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        syzbot+904752567107eefb728c@syzkaller.appspotmail.com,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: x86: Initialize tdp_level during vCPU creation
In-Reply-To: <20200527085400.23759-1-sean.j.christopherson@intel.com>
References: <20200527085400.23759-1-sean.j.christopherson@intel.com>
Date:   Wed, 27 May 2020 12:03:13 +0200
Message-ID: <875zch66fy.fsf@vitty.brq.redhat.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Initialize vcpu->arch.tdp_level during vCPU creation to avoid consuming
> garbage if userspace calls KVM_RUN without first calling KVM_SET_CPUID.
>
> Fixes: e93fd3b3e89e9 ("KVM: x86/mmu: Capture TDP level when updating CPUID")
> Reported-by: syzbot+904752567107eefb728c@syzkaller.appspotmail.com
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b226fb8abe41b..01a6304056197 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9414,6 +9414,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>  	fx_init(vcpu);
>  
>  	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> +	vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
>  
>  	vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Looking at kvm_update_cpuid() I was thinking if it would make sense to
duplicate the "/* Note, maxphyaddr must be updated before tdp_level. */"
comment here (it seems to be a vmx-only thing btw), drop it from
kvm_update_cpuid() or move cpuid_query_maxphyaddr() to get_tdp_level()
but didn't come to a conclusive answer. 

-- 
Vitaly